1. Field of the Invention
The invention relates to systems and methods for synchronizing timing of transceiver pairs and, more particularly, relates to systems and methods for controlling the synchronization of time division multiplexes of transceiver pairs by adjusting the receiver timers to synchronize the transmitter timers.
2. Description of the Related Art
Time division multiplexed (TDM) communications systems comprise multiple transmitters and receivers that share a common communication channel. Sharing of the common channel among the several users in such systems is possible because each user is allowed to use the channel only for a given period of time in a defined, repeated sequence. In this manner, time division permits the transmission of two or more signals over a common channel path by using different time intervals for the transmission of the intelligence of each message signal.
Cordless telephony is increasing in popularity, both in the United States and other countries. The conventional corded telephone consists of a base unit and a handset unit connected by an electrical cord. Because of the connection of base unit and handset unit in the conventional corded telephone, the user's range of motion is limited to the extent of the electrical cord. Cordless telephones, on the other hand, allow the user greater range of motion while using the telephone. Instead of a physical electrical cord connecting handset and base unit, cordless telephone handset and base units communicate with each other over a communication channel established by the transmission and reception of electromagnetic waves, conventionally radio waves.
Several cordless telephone system standards were previously developed and have been implemented. Most of the cordless telephone systems today conform to one of those standards. One standard, Cordless Telephony Generation 2 (CT2) interface specification for digital technology, is currently widely followed in the United Kingdom and certain European countries. The CT2 standard has been accepted by the European Telecommunications Standard Institute (ETSI) as an interim European standard. In the U.S., a different standard, the Digital European Cordless Telecommunications (DECT) standard, has been most commonly followed. It appears the CT2 standard will shortly become the European country permanent standard and that such standard will be adopted in other countries, including those of Asia and the Pacific Rim.
In any TDM communications system (whether based on the CT2 standard, the DECT standard, or other), it is a design objective to provide the best possible transceiver pair transmission and reception. In those systems, however, the several transceiver pairs that comprise the system are often located in relatively close proximity. In particular in the case of cordless telephones of those systems, relatively close proximity of the several cordless base stations can result in significant noise and interference between base stations.
This noise and interference between base stations can occur, in particular, when the several transmitters transmit at different times and/or the several receivers receive at different times. The noise and interference occurs because the transmitters generate radio frequency (RF) energy at a high level relative to the low level at which the receivers detect RF energy. If the transmitters of the system are not synchronized, a base station receiver must reject the high level transmission of neighboring transmitters in order to suitably receive the low level intended to be received by the base station receiver. It has been discovered in connection with the present invention that synchronizing transmissions and receptions among the individual telephone units in cordless telephone systems can eliminate much of the noise and interference. If the transmitters of the system are synchronized per the present invention, all transmitters transmit at the same time and all receivers receive at the same time. Therefore, interference and noise from neighboring transmitters may be eliminated because reception and transmission will always occur at different times within the system.
In the prior technology, it has been possible to program the transmit counter of each individual telephone unit of the system to be ahead in time of the particular unit's receiver counter by some arbitrary amount which is referred to as the modem delay for the system. Modem delay is comprised of two components, transmit modem delay and receive modem delay. The sum of these components is the modem delay for the particular telephone unit of the system. In the prior technology, the user had to measure the modem delay of each individual telephone unit of the system and then program each particular unit to account for the particular modem delay of the unit. As is apparent, this accounts with respect to each individual telephone unit for the modem delay experienced by that unit; however, it does not necessarily synchronize all transmissions and receptions of every telephone unit in the system.
The present invention utilizes the receiver modem delay of each individual telephone unit within a cordless telephone system to provide synchronization of transmit signals throughout the system. In this manner, the present invention eliminates base unit transmit signal interference, even among neighboring telephone units of the system. The present invention is thought to be particularly effective when implemented in systems and methods of cordless telephony. In particular, the present invention is particularly desirable in the case of cordless telephone systems comprising multiple base units and handset units and which conform to the CT2 standard. Though particularly desirable in those applications, it is believed the invention can further solve many other diverse problems found in telephone and digital communications and device systems generally, regardless of particular standards, if any, which may apply. As will be apparent, the present invention has numerous and varied application and is a significant improvement in the art.